1. Field of the Invention
The present invention relates to a liquid nebulization system, and more particularly to a vibration type liquid nebulization system.
2. Description of Related Art
Aerosol technology has been widely used in various fields such as temperature cooling, humidification, sterilization, dust suppression and medicine. As the demand for the aerosol technology has increased, many kinds of the nebulization systems have been developed for use in various fields. For example, in medicine, inhalators are used to create a fine spray of drug particles for delivery to the lungs upon inhalation, wherein such particles typically need to be below 5 μm in diameter to be effectively delivered to and absorbed by the alveoli. As another example, in agriculture, fog machines are used for greenhouse cooling and screening of excess sunlight to lower irrigation requirements, wherein the optimal fog particle diameter is about 17 μm.
Currently, nebulization systems consist of the differential pressure type, the plasma type and the vibration type, wherein the differential pressure type has been most widely applied. For example, aerosol bottles of liquid detergent, perfume and pesticide belong to the differential pressure type. Unfortunately, the differential pressure type of nebulization system is often prone to liquid leakage. However, such leakage rarely occurs in the plasma type nebulization system, making it more appropriate when leakage is unacceptable. In the plasma type liquid nebulization system, a high voltage of thousands of volts is connected to a metallic tapered rod to ionize liquid into nano-particles. However, such a design may put the user at risk of electric shock. As for the vibration type nebulization system, sonic vibration is induced by a high-frequency piezoelectrically-driven plate to produce liquid droplets. However, although no leakage or electric shock problems exist, high power consumption is often an issue with the vibration type of nebulizer.
As an example of a vibration type nebulizer, U.S. Pat. No. 5,518,179 discloses such a unit with a driving electrode that, when in operation, is driven using a self-resonant circuit with an actuator having a mechanical resonance close to 400 kHz with an amplitude of approximately 25V. The electrode circuit in combination with a self-tuning drive circuit provides excitation of the preferred vibration mode. However, a frequency tracking method is required to lock the resonant interval in order to operate the nebulization system. At the same time, a frequency tracking method is driven by a higher frequency and voltage, which are the cause of high power consumption. As another example, as disclosed in U.S. Pat. No. 6,539,937, a described nebulizer apparatus atomizes liquid solutions, delivering atomized medicine to a patient. The liquid contained in the nebulizer apparatus is vibrated at ultrasonic frequencies to atomize the liquid. The nebulization steps include adjusting the frequency at which the voltage source is supplied to the vibrating element until a measured electrical characteristic is within −2 dB of the electrical characteristic corresponding to one of the series resonant frequencies. Since the series resonant frequencies require a higher operating voltage, the problem of high power consumption also still exists. In order to solve the aforementioned problem of high power consumption, the control system for atomizing liquids with a piezoelectric vibrator as described in U.S. Pat. No. 6,439,474 discloses in a related diagram that the driving sequence of the piezoelectric actuation element is divided into alternate drive periods of 5.5 milliseconds duration, and sleep periods of from 9 to 18 seconds duration. During the 5.5-millisecond drive periods, the voltage used for driving the piezoelectric actuation element decreases exponentially from 3.3 volts down to about 1.2 volts. Thus, the piezoelectric actuating element is initially driven at a high amplitude, which has the effect of clearing liquid from its surface and initiates atomization; and then it is driven at significantly lower amplitudes, which are sufficient to maintain actuation with a minimal power consumption. The foregoing driving sequence of 5.5 milliseconds/18 seconds reduces the power consumption but causes the problem of significantly lowering the liquid nebulization amount.
Hence, it has become an issue to designers of modern nebulization systems to propose a better nebulization technique that does not increase the power consumption, or, even better, reduces the power consumption required by the nebulization system while still achieving a considerable nebulizing effect.